1. Field of Invention
The invention relates generally to a coated particulate solid compositions and, more particularly, but not by way of limitation, to a particulate inorganic solid having deposited on its surface a treatment oil containing lipids, a process for surface treating a particulate inorganic solid to produce a lipid-coated particulate inorganic solid, and a process for loading such a solid in polymer compositions.
2. Background of the Invention
Particulate inorganic pigments are used as opacifiers and colorants in many industries, including the coatings, plastics, and paper industries. In particular, titanium dioxide pigments, generally in the form of finely divided powders, are added to a polymer melt for imparting whiteness and/or opacity to the finished plastic article.
In general, the effectiveness of the particulate pigment in such applications depends on how evenly the pigment can be dispersed in the polymer melt. For this reason, pigments are generally handled in the form of a finely divided powder. Titanium dioxide, the most widely used white pigment in commerce today due to its ability to confer high opacity when formulated into end-use products, is handled in the form of a finely divided powder in order to maximize the opacifying properties imparted to materials formulated therewith. However, titanium dioxide powders are inherently dusty and frequently exhibit poor powder flow characteristics during the handling of the powder itself, especially during formulation, compounding, and manufacture of end-use products. In addition, these particles typically have a hydrophilic surface, making them difficult to incorporate in hydrophobic materials such as plastics, and thus, they require long periods of time and/or high levels of energy to achieve optimum dispersal.
To this end, chemical modification of titanium dioxide particle surfaces has been a preferred approach to achieving optimum pigment opacity as well as good flow characteristics. Surface treatment agents are typically added to the particulate titanium dioxide; however, the selection of the surface treatment agent is often a compromise between effectiveness, cost, compatibility with other additives in the plastic, and performance properties in the plastic.
A variety of treatments has been studied. For example, U.S. Pat. No. 7,601,780 discloses a silanized inorganic powder treated with a long chain fatty acid and U.S. Patent Application Publication No. U.S. 2003/0029359 A1 discloses pigment particles treated with polysaturated and unsaturated fatty acid esters. U.S. Pat. No. 6,646,037 discloses treating titanium dioxide with alkyl sulfonic acid salts, and U.S. Pat. No. 6,765,041 discloses treatment with alkyl phosphate esters. Organosilicon compounds have also been used. For instance, U.S. Pat. No. 4,061,503 discloses the treatment of particulate titanium dioxide with a siloxane compound for improving the dispersibility of titanium dioxide in pigmented and/or filled paints and plastics, and in reinforced plastic composite compositions. Also, U.S. Pat. No. 4,810,305 discloses hydrophobic pigments and fillers obtained by surface treatment with polydimethylsiloxanes and with specific organopolysiloxanes.
While there has been much research regarding the coating of titanium dioxide, further improvements are needed. To date, treatment techniques remain a compromise between cost, processability and final product properties. Despite the significant research done in this area, there remains a need for economical surface treatment of particulate titanium dioxide that provides improved handling, dispersion and final product properties.